A commonly used method to cool an airfoil component of a gas turbine engine is to duct cooling air inside the component and then vent this cooling air through a plurality of cooling holes defined through a wall thereof. Such a method is generally used to cool vanes, particularly nozzle guide vanes located at the entry of the turbine section.
The cooling holes defined in the suction side of the nozzle guide vanes are usually oriented in the stream wise direction. As such, due to the curvature of the airfoil of the vane, the cooling holes generally have a substantially large angle with respect to the surface of the vane, and are machined with the tool progressing from the outside of the vane to the inside thereof.
Determining the exact location of each hole before machining is thus based on a substantially complex outer profile of the vane, which becomes even more complex when the vanes are cast as multi-airfoil segments. As such, machining of the cooling holes generally necessitates the determination of multiple reference points on the outer surface of the vane or vane segments, substantially complex manipulation of the vane or vane segments and/or of the machining tool.
In addition, care must be exercised when machining such cooling holes in order to avoid machining too far and damaging the inner surface of the opposed wall of the vane. In particular, when the holes are machined using a laser, a material is generally inserted within the vane to absorb the laser beam when it breaks through the wall being machined to stop the laser from reaching the opposed wall. The insertion of the material within the vane, and its removal after the cooling holes are defined, increases the cost and time of the vane manufacturing process.
In addition, when the vanes are cast as multi-airfoil segments, the location of these holes can generally not be seen and hence are called blind holes or non-line of sight holes. The machining of non-line of sight holes usually requires special electrodes which increases the cost of making these holes.
Accordingly, there is a need to provide an improved cooled airfoil component.